The present invention relates to a coaxial counter-rotating rotor system, and more particularly to a pitch control system therefor.
There is an increased emphasis on the use of UAVs for performing various activities in both civilian and military situations where the use of manned flight vehicles may not be appropriate. Such missions include surveillance, reconnaissance, target acquisition, target designation, data acquisition, communications relay, decoy, jamming, harassment, ordinance delivery, or supply.
A hybrid aircraft provides the hover and low-speed maneuverability of a helicopter with the high-speed forward flight and duration capabilities of a winged aircraft. Typically, hybrid aircraft include a helicopter control surface system which provides cyclic pitch, collective pitch and differential rotation to generate lift, pitch, roll, and yaw control when operating in a hover/low-speed environment. Additionally, the hybrid aircraft includes a conventional fixed wing aircraft control surface system such as aileron, elevator, rudder and flaps to provide control when operating in a high-speed environment.
Hybrid aircraft often utilize coaxial counter rotating rotor systems to avoid the necessity of a relatively complex anti-torque rotor system. Coaxial rotor systems are exceeding effective as lift generating mechanisms. Disadvantageously, conventional dual counter rotating coaxial rotor systems require a relatively large separation between each rotor system. Such a separation is required to provide adequate cyclic and collective pitch control though swashplate articulation and differential rotor blade flapping to assure clearance therebetween regardless of aircraft maneuver. Disadvantageously, application of such rotor spacing to a hybrid UAV type aircraft may result in a relatively tall aircraft with associated storage and transportation limitations.
Accordingly, it is desirable to provide a coaxial counter-rotating rotor system for a hybrid aircraft which generates sufficient cyclic and/or collective pitch inputs within a compact, closely spaced structure.